This invention relates to a mechanism for actuating an opening and shut off valve for the outflow orifice in the bottom of a stand-by hopper of a loading installation for a shaft furnace. More particularly, this invention relates to a new and improved valve actuating mechanism comprised of two registers, each in the form of a cylindrical or spherical cap and pivoting in opposite directions about their common suspension axles so as to define a central outflow orifice symmetrically variable about the central outflow axis of the hopper; and which has drive means acting on at least one of the shutters.
The present invention is particularly well suited for use with a valve for a stand-by hopper for an installation of the central loading type, such as that described in the patent EP-B1-0062770 corresponding to U.S. Pat. No. 4,514,129, assigned to the assignee hereof, all of the contents which are incorporated herein by reference. This stand-by hopper acts to fill (as quickly as possible) a lock chamber which is arranged immediately below the hopper and from which the flow of loading material towards the means of a distribution in the furnace (which is usually a rotary or oscillating chute), is adjusted. The lock chamber possesses a cylindrical outflow pipe, the orifice of which is equipped with a proportioning valve of the type described above. A mechanism of the above-described type for actuating such a proportioning valve is disclosed in the document EP-B1-134,918 corresponding to U.S. Pat. No. 4,570,900, which is assigned to the assignee hereof, all of the contents of which are incorporated herein by reference.
Unfortunately, this known valve actuating mechanism cannot be used for the valves covered by the present invention. One of the reasons for this is that the stand-by hopper has to be emptied as quickly as possible in order to curtail any idle time during loading. For this reason, its outflow orifice must be as large as possible; and the valve associated with its outflow orifice must similarly be designed to allow for this large size. However, the proportioning valve described in U.S. Pat. Nos. 4,514,129 and 4,570,900 which is associated with the outflow pipe of the lock chamber is of much smaller size. In particular, these known valves consist of two registers or shutters in the form of spherical caps which are supported directly by their pivot axles. It is these pivot axles which are actuated by the drive means.
In contrast, the valves for which the present invention is intended must have a larger radius of curvature. This is because they are not associated with a cylindrical outflow pipe (as in the prior art), but are instead associated with the bottom of a funnel shaped hopper. Because of the funnel shaped hopper, the two registers cannot each pivot 90.degree.. Consequently, the two shutters must be mounted on supporting arms pivoting about the axis of rotation of the registers; and because of the size of the registers and that of the outflow orifice, these supporting arms have to be relatively long. As a result, if the drive means were to act on the rotary axle of the supporting arms in order to actuate the registers, there would be a loss of force due to the negative lever effect caused by the relatively long supporting arms. In view of this loss and because of the size of the registers, the drive means would have to be very powerful and their suspension would have to be constructed accordingly.
Moreover, it will be appreciated that, in recent installations, the stand-by hopper together with its shut off valve are designed to be rotatable about its vertical axis in order to prevent the effect of segregation of the particles during filling. Consequently, the mechanism for actuating the known valves associated with the outflow pipe of the lock chamber is not suitable for a rotating hopper because of the lateral bulk of the control mechanism.